This application is based on Patent Application No. 2000-369105 filed Dec. 4, 2000 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink jet printing apparatus, and more particularly to an ink jet printing apparatus and an ink jet printing method which eject ink by an energy generated by an electrothermal transducer.
2. Description of the Related Art
Generally, the ink jet printing apparatus performs printing by relatively moving an ink jet print head over a print medium while ejecting ink from the head. In the ink jet printing apparatus, a quality of the printed result depends on such factors as a control of a relative speed between the print head and the print medium, a control of an ejection timing associated with the relative speed control, and a stability of power supply to the print head. The ink jet printing apparatus is classed into a serial type and a full-line type according to the type of the print head used. The serial type is a widely used printing apparatus in which the print head is reciprocally moved in a direction crossing a print medium feeding direction while ejecting ink from the head.
There are several types of print head, including one which ejects ink by activating a piezoelectric element and a so-called bubble jet type which generates a bubble by an instant surface boiling and ejects ink by using a pressure of the bubble as an ejection energy. The print head of the bubble jet type causes the surface boiling of ink by energizing a heater installed near an ink ejection nozzle in an ink path.
In such ink jet printing apparatus, it is important in keeping the print quality satisfactory that the energy for ejecting ink be supplied stably at all times to eject the ink under the same condition and thereby produce uniform ink droplets. However, the number of heaters that are energized simultaneously is not fixed but changes according to a duty ratio of image data. Hence, the heater driving condition varies, affected by voltage variations due to changes in an output current of the power supply and by variations in voltage drop due to resistance component changes in a power supply system.
Hence, in conventional ink jet printing apparatus, it is common practice to enhance the precision of power supply output and construct the power supply system with as little loss as possible so that the printing apparatus can be operated in a range that can meet the ejection requirements.
As color image handling is made easy by increased speeds of personal computers in recent years, the amount of data to be processed and the processing speed are increasing rapidly.
Although the speed of the ink jet printing operation can be enhanced by increasing the ink ejection frequency and the number of nozzles that can be energized simultaneously, this gives rise to a problem that a change in the number of nozzles that are energized simultaneously in the actual printing operation becomes large. That is, of the nozzles that can be energized at one time, the number of nozzles used in the actual printing operation changes according to the image data being printed. When the number of nozzles that can be energized simultaneously is increased to enhance the printing speed as described above, the number of nozzles energized simultaneously varies greatly depending on the image data.
For example, when printing a black solid image, all the nozzles that can be energized for simultaneous ink ejection are used. When printing a low-duty image, such as lines, only a part of the available nozzles are used for simultaneous ink ejection. In this way, the number of nozzles that are driven simultaneously varies depending on the image data. This variation becomes more conspicuous as the total number of nozzles in the print head increases. The difference (or change) in the number of nozzles that need to be driven simultaneously results in a difference (or change) in the current that needs to be supplied to the ejection energy generating means such as heaters.
A circuit for supplying electricity to the ink jet print head for ink ejection has a resistance component, such as contact resistance with a connector and its own wiring resistance. Hence, when the heaters are in a conducting state, the voltage applied to the print head drops in proportion to the current because of the heater resistance component. If the current changes greatly as a result of a change in the number of simultaneously energized nozzles, the drive voltage applied to the heaters of the print head also changes, posing a problem that the ink ejection cannot be performed under the same condition. That is, as the change in the drive voltage increases, the resulting variations in the ink ejection condition greatly influence the print quality, which is detrimental to improving the speed of the printing operation. Therefore, if an ink ejection control which can keep the ejection condition from changing according to the print data is possible, the speed of the printing operation can be increased.
To realize such an ink ejection control, image recording apparatus have been proposed and practiced, which include one comprising a count means for counting print data to monitor the number of nozzles that are actually energized for ink ejection and an output voltage changing means for changing the output voltage of a power supply according to the count value, and one comprising the count means, a variable resistance load means for changing a resistance in a power supply circuit to the print head, and a control means for setting a value of the variable resistance according to the count value.
In these printing apparatus, a control is made in such a way that when the number of simultaneously energized nozzles is large, the resistance value of the variable resistance load means is reduced and that when the number of simultaneously energized nozzles is small, the resistance value is increased. This arrangement can control the voltage drop caused when the current flowing through the heaters passes through this variable resistance load means, thereby keeping the voltage applied to the heaters during ink ejection constant and the ejection condition uniform.
The image forming apparatus described above that counts the number of simultaneously energized nozzles, however, has the following problem. That is, although the count value can be monitored easily since it is a digital quantity, the variable resistance load means easily experience characteristic variations and degradation of characteristics over time, so that simply performing the control based on the energized nozzle count value cannot achieve an accurate control nor a satisfactory print quality.
An object of the present invention is to provide an ink jet printing apparatus and method with an inexpensive arrangement that allows a stable supply of an appropriate voltage to heaters without requiring a variable resistance load means or a power supply voltage changing means.
According to one aspect the present invention provides an ink jet printing apparatus which comprises: a plurality of nozzles arrayed in a print head; a plurality of energy generating means for generating an ejection energy to eject ink from the nozzles, the plurality of energy generating means being divided into a plurality of blocks; and a drive control means for supplying an energy through an energy supply path to the energy generating means in each block simultaneously; wherein the drive control means supplies an energy to at least a part of the energy generating means making up each block through a plurality of different kinds of the energy supply paths.
That is, the Ink jet printing apparatus of this invention has a plurality of nozzles arrayed in a print head; and a plurality of energy generating means for generating an ejection energy to eject ink from the nozzles; wherein the energy generating means have a plurality of energy supply paths and a drive control means for simultaneously driving a part of the plurality of the energy generating means. This apparatus is characterized in that the plurality of the energy generating means connected, in one-to-one relationship, to n different supply paths constitute one block and that the drive control means is so arranged as to simultaneously drive as the same block the energy generating means each forming an element of each one of different groups.
According to another aspect, the present invention provides an ink jet printing apparatus which comprises: a plurality of nozzles arrayed in a print head; and a plurality of energy generating means for generating an ejection energy to eject ink from the nozzles; wherein the print head having the energy generating means has a wiring pattern formed on a heater board therein in such a way that wiring resistances of energy supply paths running to different nozzles are equal.
According to still another aspect, the present invention provides an ink jet printing apparatus which comprises: a plurality of nozzles arrayed in a print head; and a plurality of energy generating means for generating an ejection energy to eject ink from the nozzles; wherein the print head having the energy generating means is mounted on each of a plurality of carriages that move on different moving paths, and a long power supply path connecting to the print heads mounted on one of the carriages is formed with a wire material of a lower electric resistance than that of a wire material of a short power supply path connecting to the print heads mounted on another carriage.
According to a further aspect, the present invention provides a printing method which comprises the steps of: dividing a plurality of energy generating means into a plurality of blocks, the energy generating means being adapted to generate an ejection energy to eject ink from nozzles; and simultaneously energizing the energy generating means in each block to perform printing; wherein a control is performed to supply an energy to at least a part of the energy generating means making up each of the blocks through a plurality of different kinds of energy supply paths.
As described above, with this invention, since a stable supply of electricity can be made through a plurality of head drive power supply paths, without being affected by a change in the number of nozzles that are simultaneously energized, the ink ejection condition remains stable assuring the printing of high-quality images.
Further, even when the head drive power supply paths differ in length, their wiring resistances can be made equal, keeping the ejection conditions uniform among different nozzles and thus assuring the printing of high-quality images.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.